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Physics · PYQ NEET UG 2018
हिन्दीThe refractive index of the material of a prism is \( \sqrt{2} \) and the angle of the prism is \( 30^\circ \). One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is
Correct answer · Option 2
\( 45^\circ \)
Explanation
For the light ray to retrace its path from the silvered surface, it must strike normally, so angle of refraction inside is \( r_2 = 0 \). Thus \( r_1 = A = 30^\circ \). Using Snell's law, \( 1 \cdot \sin i = \sqrt{2} \sin(30^\circ) = \frac{\sqrt{2}}{2} = \frac{1}{\sqrt{2}} \), which gives \( i = 45^\circ \).
